The new rules, which are expected to take effect in the next six months, are part of an effort to placate concerns over underage fighters joining the ranks of the West Papua Liberation Army, and comes as the independence movement struggles to gain ground with the international community.

On Monday, the United Liberation Movement for West Papua (ULMWP) claimed it was taking political leadership of the Liberation Army and the two other main rebel groups in Papua. According to the ULMWP, the three will form a new grouping dubbed the West Papua Army and will undertake military reforms.

"We want to follow international law. We also must keep little boys in very clear position," said Jacob Rumbiak, an Australia-based ULMWP spokesperson. He said the changes would restrict active combat operations by the West Papua Army to adult fighters, although he added children would still be trained for combat.

A release on Monday from the office of the ULMWP chair, Benny Wenda, said it was the first time the three major rebel factions had come under a single arm.

"Politically and militarily we are united now. The international community can now see without a doubt that we are ready to take over our country," he said.

But undermining the new united front, the Liberation Army released a counter-statement on Monday, saying it was "not a part of ULMWP or the West Papua Army." The statement said Mr Wenda's claims were "fabrications and lies".

Experts said the ULMWP assuming political leadership over armed forces was unlikely to carry much sway with rebels already operating with little oversight, especially within the Liberation Army, which is engaged in a chaotic war with Indonesian forces in Nduga regency.

"I don't know if it can be applied anytime soon given the nature of the Liberation Army is quite fragmented since the 1960s," Hipo Wangge, a researcher at Marthinus Academy in Jakarta, said of claims the West Papua Army would end the use of child soldiers.

A spokesperson for the Liberation Army couldn't be reached for comment on the proposed regulations.

Victor Mambor, the editor of Papuan news site Tabloid Jubi, said a meeting in Papua New Guinea last year between the three armed groups and the Liberation Movement had ended with some members "unhappy" over the outcome.

Since then, the Liberation Army has found itself at the centre of a war with Indonesia after its fighters massacred at least 16 Indonesian construction workers in Nduga in December, in the worst bout of violence to strike Papua in years. Hundreds of Indonesian military and police have been deployed in a hunt for the rebel group.

Rights groups have documented a widespread displacement of civilians from Nduga, including hundreds of children who have been forced to take shelter in displacement camps in nearby cities. In April, the Irish human rights group Front Line Defenders said more than 32,000 people had been displaced from the regency since December.

Still, the formation of the West Papua Army shows how Papuan rebel groups are being leveraged to win international support for the independence movement.